Update on the Regional Assessment of Gas Potential in the Devonian Marcellus and

Ordovician Utica Shales in New York

Richard Nyahay, James Leone, Langhorne Smith, John Martin, and Daniel Jarvie

Assessing unconventional shale gas plays in New York

• Identify high gas potential fairways using same geochemical methods applied to the Barnett and other successful shale gas plays

• These include TOC, vitrinite reflectance, hydrogen index and transformation ratios

• Create new structure and isopach maps of shale formations and potential gas producing intervals

Two Similar Black Shales: Devonian Marcellus and Ordovician Utica

• Deposition of both shalesfollowed lithosphericdownwarping associated with tectonic loading

• Both shales terminated by shallow shelf carbonates

• Both shales thicken to the east

The Ordovician Utica Shale

(Goldman, et al 1994)

Trenton Limestone in blue colors is time-equivalent to Utica Shale in brown colors: Primarily interested in Flat Creek and to a lesser

extent the Dolgeville Member

Tren

ton

Utic

a

Utica East-West Cross SectionU

tica

Dolgeville

Flat Creek

Trenton

Black River

Tren

ton

Utic

aTr

ento

n

Indian Castle

Utica Structure Contour Map

Utica gets deeper to the south

Utica Isopach Map

Utica formation thickens to the east

Utica Flat Creek Member

• Lowermost member of the Utica Formation• K-bentonites and graptolites used to match

key successions(Goldman, et al., 1994)• Dark gray to black, variably calcareous

shale with minor thin beds of argillaceous micrite and biomicrite (Lehmann, et al. 1995)

• Bounded by Dolgeville member on top

Utica - Flat Creek Member

Vertical calcite filled veins cutting Flat Creek Member in Chuctanunda Creek, Florida, NY

Utica Flat Creek Isopach Map

Utica Flat Creek member thickens to the southeast –In the end, this is likely to be the Utica Fairway map

Utica - Dolgeville Member

• Interpreted as a slope facies peripheral to the Trenton platform

• Tabular ribbon limestones and dark gray to black shale beds

• Several geochemically correlated K -bentonites• Bounded on top by Thruway unconformity • Slump folds occur immediately below the

unconformity• Folds are dominantly asymmetrical with a

westward vergence

Utica – Dolgeville Member

Asymmetrical slump fold in Dolgeville

Utica Dolgeville Isopach Map

Dolgeville thickens to southeast

Utica - Indian Castle Member

• Uppermost member of the Utica Formation blankets all of western NY

• Thin layers of fossil debris, phosphatic debris and quartz

• Condensed beds• K-bentonites used to match key successions• Sharp contact with underlying Steuben limestone,

more subtle contact where it overlies Dolgeville• Divided into the lower and upper sections

(Baird and Brett, 2002)

Utica - Lower Indian Castle Member

Characteristically hard, blocky shale with interbedded, tabular, impure limestone

Utica Upper Indian Castle

Monotonous fissile, black shale and silty black shale

Geochemical Study

• Using geochemistry in an attempt to define a general fairways for exploration in Utica and Marcellus

• Using the same Rock-Eval approach Jarvieet al used for the Barnett Shale

Used cuttings from 31 wells, and samples from 12 cores, 5 outcrops

Gas Production from Shales

• Gas production from tight shales requires maturation and cracking of oil that has been generated from live organic matter - need to have at least 2 percent TOC to begin with

• With increasing maturation carbon and hydrogen are lost from shale due to hydrocarbon generation

• Increasing thermal maturity therefore leads to decrease in TOC and hydrogen values

• Want shales with decent original TOC, with evidence that significant amounts of gas has formed from that TOC during thermal maturation

Geochemical Measurements

• TOC = Total organic carbon (%)• Live carbon including S1 (oil and gas present in

shale) and S2 (remaining kerogen)• Tmax = The temperature at peak evolution of S2

hydrocarbons from Rock Eval• Ro% = Vitrinite Reflectance (calculated from

Tmax)• HI= Hydrogen Index (S2 x100)/ TOC• TR= Transformation or conversion ratio calculated

from hydrogen index (HI)

Geochemical TOC Data

• Indian Castle < .5%• Dolgeville .5 - 1.5% • Flat Creek 1.5 - 3%

In Jarvie, et al., 2005 study TOC from cuttings were 2.36 times lower than samples from core; therefore this same dilution effect would be seen on other geochemical parameters

Productive shales are generally >2% TOC

Utica TOC Map

TOC increases to the SE as Utica (Flat Creek and Dolgeville members) also thickens in that direction

TOC Utica Cross Section

TOC increases in Dolgeville and increases more in the Flat Creek member

DispersedOrganicMatter:

the “source”of

oil + assoc. gas

Rock Sample

TOC

Live Carbon

Organic Matter (Kerogen)Oil

Gas

Total Organic Carbon (T.O.C.)

Dead Carbon

Dead Carbon

Rock-Eval TerminologyJarvie, 1991

TOC

Distribution of Organic Matter in Rock Sample (low maturity)

Live Carbon

Organic Matter (Kerogen)Oil

Gas

Total Organic Carbon (T.O.C.)

Dead Carbon

Dead Carbon

Oil Prone Gas Prone

S2 (and Tmax)S1 S4

Rock-Eval Terminology

Rock-Eval analysis - terminology

Jarvie, 1991

If S1 and S2 are very low, this means that almost all remaining carbon is dead carbon – the rock cannot and will not generate any more hydrocarbons

Rock-Eval or SR Analyzer “Pyrogram”

S1

S2

Tmax

Temperature trace (nonisothermalat 25oC/min)

300oC

600oC

Time (mins.)

Yield

S4

Jarvie, 1991

Oil gas present

Kerogen

•S1 = Free volatile hydrocarbons thermally flushed from a rock sample at 300°C•S2 =products that crack during standard Rock-Eval pyrolysis temperatures 300°C-

600°C

Rock-Eval or SR Analyzer “Pyrogram”

S1

S2

Tmax

Temperature trace (nonisothermalat 25oC/min)

300oC

600oC

Time (mins.)

Yield

S4

Jarvie, 1991

Oil gas present

Kerogen

In order to get a reliable Tmax, it is necessary that S2>S1 and the value of S2>0.2 - If S1>S2 or S2 has very low values (<0.2) that means that

there is very little remaining live carbon (kerogen or oil and gas)

432Tmax TOC S2 HI

5.21 19.80 380435 4.53 13.45 297437 4.11 10.27 250443 3.77 5.88 156455 3.41 1.81 53470 3.32 1.36 41

CONVERSIONTO OIL and

GAS

INCREASINGTHERMALMATURITY

89%36%

Remainingpotentialdecreases

Tmax increases

TOC HI

Experimental Conversion of Barnett Shale

Utica

2.3 <0.2 <10? Utica

Values so low it is hard to pick Tmax

Total Organic Carbon (TOC)

OMOilGas

Maturation of Organic Matter – modified from Jarvie

Total Organic Carbon (TOC)

O.M.OilGas

Dead Carbon

Dead Carbon

DeadCarbon

Total Organic Carbon (TOC)

OMOil Dead CarbonGas

Dead CarbonTotal Organic Carbon (TOC)

Dead Carbon

Utica Shale –almost all TOC dead carbon

Incr

ease

d M

atur

atio

n

Barnett Shale has samples with Barnett Shale has samples with range of maturation valuesrange of maturation values

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14 16

TOTAL ORGANIC CARBON (TOC, wt.%)

REM

AIN

ING

HYD

RO

CA

RB

ON

PO

TEN

TIA

L (m

g H

C/g

Roc

k)

Type I Oil Proneusu. lacustrine TYPE II Oil Prone

(usu. marine)

Mixed Type II / IIIOil / Gas Prone

Type IIIGas Prone

OrganicLean

DryGas Prone

Barnett ShaleMaturation

Trend

Utica Samples

Utica Tmax and Vitrinite Reflectance (Ro)

• Tmax is the temperature where S2 peaks• Because >95% of the S2 values in the Utica are too

low and/or <S1, the Tmax values are unreliable in the Utica Shale

• Tmax can be used in some cases to obtain a calculated value for vitirinite reflectance (Ro) by the formula Ro=0.0180*Tmax-7.16

• Because Tmax is unreliable in the Utica, it is not possible to calculate reliable values for Ro

Hydrogen Index

• Hydrogen Index (HI) is a calculation to determine the amount of hydrogen remaining in the shale

• HI = (S2*100)/TOC • HI decreases as thermal maturity increases

because S2 goes down• Again, S2 is uniformly very, very low in Utica so

the HI values largely driven by TOC –• Lower values are generally thought to be better in

Utica as they represent higher original TOC

Utica Flat Creek HI Map

Lowest values occur where TOC was highest in Flat Creek and Dolgeville

Artifact

Transformation Ratio

• Evaluates the conversion directly by measuring changes in the kerogen (organic matter) yields

• In order to calculate this ratio, you need the present day Hydrogen index (HIpd) and original Hydrogen index (HIo) (see Jarvie, et al., 2007 for formula)

• Areas with highest potential for production have values approaching 1, lower values = lower potential

Utica Flat Creek Transformation Ratio Map

Best TR values occur where the Flat Creek and Dolgeville occur – all of these values driven by higher TOC in those members

Wells with good Utica shows and TR Map

Inside the blue lines as defined by the transformation ratio might be a productive fairway for Utica Flat Creek prospects

New Utica wells and TR map

Inside the blue lines as defined by the transformation ratio are the newly drilled wells – awaiting results

Utica Flat Creek Isopach Map

The Utica Fairway is probably best defined by the Flat Creek Mbrisopach map – All of the Utica is supermature; the Flat Creek had the highest original TOC which drives HI and TR maps

feet

The Devonian Marcellus Shale

Primarily interested in Union Springs and Lowermost Oakta Creek Members

Marcellus Union Springs

• Organic rich thinly bedded blackish grey to black shale with thin silt bands

• The member is between the Cherry Valley and Onondaga Limestone

• Characterized as pyritiferous; farther east the Union Springs becomes the Bakoven member that becomes darker, less organic and has few limestone members

• Lenses in and out in localities in far Western New York

Marcellus Union Springs

Union Springs with vertical calcite filled fractures in the Onesquethaw Creek, Albany County, NY

Marcellus Cherry Valley

• Consists of skeletal limestones and shalyintervals

• Westward thinning of the Marcellus Formation in western and central New York leads to the condensation and union of the Cherry Valley limestones with limestones in the upper part of the Union Springs

Marcellus Cherry Valley

Cherry Valley dark shaly interval and limestone near Cherry Valley, NY

Marcellus Oatka Creek

• Upper member of the Marcellus Formation in Western and central New York

• Becomes Cardiff and Chittenango members in Central and Eastern New York

• Is confined in Western New York by Stafford and Onondaga limestones

• Farther east it is between the Stafford and Cherry Valley limestones where it is present

• Dark grey to black organic rich shale

Marcellus Oatka Creek

Oatka Creek shale in Oatka Creek, LeRoy, NY

Marcellus Isopach

Marcellus thickens to the east

Marcellus Structure Contour Map

Marcellus has a general east-west strike is gently dipping south

Map of Marcellus Geochemical Locations

33 wells, 2 cores, 9 outcrops

Marcellus TOC Map

TOC much higher in Marcellus than in Utica (up to 12%) TOC values are highest in central part of state and decrease to east

Marcellus Union Springs TOC Map

TOC in the Union Springs increases from the western part of NY to the central eastern side of NY

Marcellus Oatka Creek TOC Map

TOC increases in the Oatka Creek to the northeast and west-northwest

TOC Marcellus Cross Section

TOC increases in Oatka Creek and the Union Springs member

Tmax (deg C°) Marcellus

About half of the S2 values in the Marcellus can be trusted for Tmaxvalues – using these, Tmax increases to east as would be expected

Vitrinite Reflectance Calculation

• Vitrinite refelctance (Ro) is a measure of thermal maturity that can be done directly on plant matter

• Ro can be estimated from reliable Tmax data using the following calculation

• Ro (%)=(0.0180*Tmax)-7.16• The Tmax data in the Marcellus is much better than

the Utica – about half the points have useable S2 values

Vitrinite Reflectance (Ro%)

• Low maturity source rocks 0.0 – 0.55%

• Oil window 0.55% -1.0%• Condensate - wet gas

window 1.0 %- 1.40%• Dry gas window > 1.40%

• Low maturity source rocks 0.0 - 0.55%

• Oil window 0.55%- 1.15%• Condensate – wet gas

window 1.15% -1.40%• Dry gas window > 1.40 %

Well Cuttings Core

based on Jarvie, et al, 2005

Marcellus (Union Springs) Ro%

Optimum Ro% for Marcellus Union Springs is in the central and eastern New York

Marcellus (Oatka Creek) Ro%

Optimum Ro% for Oatka Creek is in eastern side of basin – based on this it is best to avoid western half of state

Marcellus Union Springs HI Map

Union Springs HI decreases to the east

Marcellus Oatka Creek HI Map

Oatka Creek HI decreases from west to east

Marcellus Oatka Creek Transformation Ratio Map

Marcellus Union Springs Transformation Ratio Map

New Marcellus wells and the TR Map

The geochemistry work that we have done suggest that the shales in this area are favorable - some wells drilled here have not produced

Marcellus• Some wells, such as the Beaver Meadows well,

were drilled in what is the geochemical fairway for Marcellus but were not completed and are assumed to be dry holes. Why?

• Other aspects may be equally important – completion/frac practices need to be refined – may need certain silica content– too much TOC?– Overcooked?

• More work is needed

Utica and Marcellus fairways

They overlap in eastern side of basin

Future Work

• Calculate and make maps of original TOC, S2 and HI

• Get analysis of gas samples from newer wells whenever possible

• Get mineralogy data for shales• Resample areas where data is questionable or

missing and test conclusions with new samples in fairways

• See what happens with newer wells in fairways that have new drilling/completion/frac concepts

Conclusions• The Marcellus and Utica Shales both contain fairways that

are favorable to gas exploration based on geochemical data• Both fairways occur in overlapping areas in the eastern

Southern Tier of the State where there are not many wells drilled to date

• Wells with good shows occur in predicted fairways• Within the Utica Shale, the Flat Creek and to a lesser

extent the Dolgeville Members, which both thicken to the east and pinch out to the west have the best potential

• In the Marcellus Shale, the Oatka Creek and Union Springs Members have the best potential

• The Marcellus is organically richer than the Utica

Acknowledgements

• John Martin for NYSERDA financial support

• Fortuna Energy • EOG Resources• Jay Leonard of Platte River Associates for

geochemical data on eastern most Utica well cuttings